1. Field of the Invention
The present invention relates to a device for testing units containing electrical circuits, whereby an interpretation circuit is provided for the interpretation of unit-under-test signals emitted by the unit being tested at a test output, and whereby a load circuit is provided for loading the output of the unit with a definable load.
2. Description of the Prior Art
Computer-controlled testing installations require programmable drive circuits and programmable interpretation circuits at every test connection for a fully-automatic testing of SSI, MSI, LSI and VLSI modules. The drive circuit must be in a position to both transmit the corresponding signal level parameters required by the data sheet of the unit being tested to an input of the unit and to execute the change of signal level of the test signal to be applied to the unit being tested with the required edge steepness. Finally, in the case of a bidirectional test connection, for example given a tri-state bus driver, the output of the drive circuit must be able to rapidly shut off to high resistance state or, respectively, switch back on. When the test connection is an output, then this must be able to be loaded according to the data sheet of the unit being tested and, in addition, the output signal of the unit being tested must be able to be interpreted chronologically and amplitude-wise by way of a suitable interpretation circuit with reference to programmable reference voltages and sampling clocks. This is the reason why a programmable load circuit and a programmable interpretation must be provided in the evaluation circuit.
Since units are to be tested in different circuit technology, for example ECL technology, TTL technology or MOS technology, etc, with the testing installation, the drive circuits and evaluation circuits must programmably cover broad current and voltage ranges in order to be universally useable. Further, strict-frequency requirements are made of such circuits in order to also be able to undertake dynamic tests given high test signal rates.